JPH04132047A - Magnetic recording/reproducing device - Google Patents

Abstract

PURPOSE:To obtain the detector of few errors against the variation of an output signal by deciding likelihood by the synthetic metric value of a signal which is the output signal from a magnetic head sampled as it is and the signal sampled after passing it through a filter. CONSTITUTION:A signal processing circuit 1 which generates the signal of the output signal from the magnetic head sampled as it is at bit intervals, one signal parallel processing circuit 2, at least, which generates the signal generated by branching the output signal from the magnetic head and sampling it at the same bit intervals after passing it through the filter, and a signal estimation circuit 3 which generates the assumed data of each output signal are provided. Beside, a metric calculation circuit 4 which calculates the metric of an error from an estimated value based on each assumed data, an addition circuit 5 which adds two metric values, at least, calculated by the metric calculation circuit 4 and generates the synthetic metric value, and a likelihood decision circuit 6 which decides the likelihood by the synthetic metric value are provided. Thus, the detection of low error rate against the variation of the output signal due to a recording medium can be obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding a magnetic recording/reproducing device that decodes a reproduced signal from a magnetic recording medium using a maximum likelihood detection method, the advantages of the maximum likelihood detection method even if there are fluctuations in the output signal from the magnetic recording medium. With the aim of providing a signal processing method that can realize the same characteristics in magnetic recording, a magnetic recording and reproducing device decodes the reproduced signal from a magnetic recording medium using a maximum likelihood detection method.The output signal from the magnetic head is sampled as it is at bit intervals. The output signal from the magnetic head is branched from the signal processing circuit that creates the signal.
at least one signal parallel processing circuit that produces signals sampled at similar bit intervals after passing the branched signal through a filter; and generating assumed data for each signal output from the signal processing circuit and the signal parallel processing circuit. a metric calculation circuit that calculates a metric that is an error between each signal output from the signal processing circuit and the signal parallel processing circuit and an estimated signal value based on assumed data from the signal estimation circuit; , an addition circuit that adds at least two metric values calculated by the metric calculation circuit to create a composite metric value, and a likelihood determination circuit that determines the likelihood based on the composite metric value from the addition circuit.

[Industrial application field]

The present invention relates to a magnetic recording and reproducing apparatus, and more particularly to a magnetic recording and reproducing apparatus that decodes a reproduced signal from a magnetic recording medium using a maximum likelihood detection method.

Many methods for detecting signals reproduced from magnetic recording have been proposed so far. Most conventional detection methods basically perform demodulation using the signal obtained by sampling the reproduced signal, but in both cases, the S/N ratio and resolution of the reproduced signal may deteriorate due to noise from the reproduction circuit, etc. A major challenge is how to achieve detection with a low error rate and a low S/N ratio.

Therefore, a magnetic recording/reproducing apparatus using a maximum likelihood detection method using a Viterbi decoder has been proposed, which provides high reliability even with a low S/N ratio. However, in magnetic recording and reproducing devices that employ this maximum likelihood detection method, the S/N ratio may deteriorate due to output amplitude fluctuations specific to magnetic recording and the presence of media defects.
This improvement is desired.

[Prior Art] Currently, the demodulation method of reproduced signals from magnetic recording media is a method that generally captures the peak point of the head output signal, but it has limitations in high-density recording such as waveform interference and SZN. have. As an alternative method, the maximum likelihood detection method (detection method using a Viterbi decoder), which is being intensively researched in the communications field, is attracting attention as it can significantly reduce the S/N ratio compared to conventional detection methods. has been done.

As an application of this maximum likelihood detection method to magnetic recording,
K. Kobayashi's paper rApplication
on of Probabilistic Decodi
ng to Digital MagneticRec
ording 5yste+*; IBM J, RE
S, DEVELOP, Jan.

1971J (Application of stochastic demodulation to digital magnetic recording systems - IBM Japan Development Research Institute, 1971.1
month) etc. are known.

[Problem to be solved by the invention]

However, when the maximum likelihood detection method is applied to magnetic recording, SZN increases geometrically due to output amplitude fluctuations specific to magnetic recording (modulation caused by non-uniformity of the magnetic film of the recording medium) and the presence of media defects. The problem is that it deteriorates. In other words, the maximum likelihood detection method is effective for a signal in which ordinary random noise is superimposed on the original signal, but when the random noise peculiar to the reproduced signal from a magnetic recording medium, the output fluctuation of the medium, etc. A signal on which output fluctuations due to the presence of medium defects are superimposed is regarded as noise in the maximum likelihood detection method, resulting in a problem that the SZN deteriorates.

The purpose of the present invention is to solve the problems of the conventional maximum likelihood detection method with respect to the output amplitude fluctuation peculiar to magnetic recording caused by modulation caused by the non-uniformity of the magnetic film of the recording medium and the presence of medium defects. To provide a magnetic recording and reproducing device that can realize detection with a low error rate for fluctuations in output signals caused by recording media specific to magnetic recording, and can realize the excellent characteristics of the maximum likelihood detection method even in magnetic recording. It is in.

[Means to solve the problem]

The configuration of a magnetic recording/reproducing apparatus according to the present invention that achieves the above object is shown in FIG. As shown in this figure, the magnetic recording and reproducing device of the present invention is a magnetic recording and reproducing device that decodes a reproduced signal from a magnetic recording medium using a maximum likelihood detection method, and samples the output signal from the magnetic head as it is at bit intervals. at least one signal parallel processing circuit 2 that branches an output signal from a magnetic head, passes the branched signal through a filter, and then produces a signal sampled at similar bit intervals; signal processing circuit l
and a signal estimation circuit 3 that generates assumed data for each signal output from the signal processing circuit 1 and the signal parallel processing circuit 2; and a signal estimation circuit 3 for each signal output from the signal processing circuit 1 and the signal parallel processing circuit 2. a metric calculation circuit 4 that calculates a metric that is an error with an estimated signal value based on assumed data from the metric calculation circuit 4; and an addition circuit that adds at least two metric values calculated by the metric calculation circuit 4 to create a composite metric value. 5, and a likelihood determination circuit 6 that determines the likelihood based on the composite metric value from the addition circuit 5.

[Effect]

According to the magnetic recording and reproducing apparatus of the present invention, the output signal from the magnetic terminal is branched, one of which is sampled at the same bit interval as it is, and the other is sampled at the same bit interval after passing through a filter. After this, for the two types of signals, a metric, which is the error between the two types of signals and the estimated signal value based on the assumed data corresponding to each signal, is calculated, and the calculated metric values are added to form a composite metric. The likelihood is determined and the maximum likelihood output becomes the detection output.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The maximum likelihood detection method that has been proposed in the past is basically amplitude detection, and in magnetic recording, the output modulation caused by the recording medium described above directly affects the signal S/N ratio. Therefore, in the embodiment shown in FIG. 2, in order to solve this problem, the differential value of the head output signal is detected, and five-likelihood detection is performed using two of the amplitude value and this differential value.

The magnetic recording and reproducing apparatus of this embodiment includes a magnetic head 21, a low-pass filter 22, two samplers 23, 26, a differentiator 25, two metric calculators 24, 27, and an adder 2.
8. It is made up of a path selector 29, a path storage register 30, two impulse response stores 31.33, and two signal estimators 32.34.

In FIG. 2, the head output from the magnetic head 21 is filtered with noise by a filter 22, typically a low-pass filter or the like, and then branched into two branches, one of which is sent to a sampler 22.
and the other is differentiated by a differentiator 25 and then input to a sampler 26. In the sampler 23, the magnetic head 21
The output signal from the magnetic head 21 is directly sampled at bit intervals using the clock signal CLK to create a signal a, and the sampler 26 generates a signal a by sampling the differential waveform of the output signal from the magnetic head 21 at bit intervals using the same clock signal CLK. Made. Signal a produced by sampler 23 and signal A produced by sampler 26 are input to metric calculators 24 and 27, respectively.

Signals a and b are both digital values.

In the impulse response memory 31.33, FIG. 4(a),
As shown in (b), a sample value e obtained by sampling the head output for a signal "1", that is, an isolated waveform at a sampling interval T, and its differential value f are stored, respectively. The sample value e becomes the estimated signal a′ produced by the signal estimator 32 and is input to the metric calculator 24, and the differential value f of the sample value e becomes the estimated signal b′ produced by the signal estimator 34 and is used for metric calculation. The signal is input to the device 27. This signal estimator 32.34 uses the sample value e from the impulse response memory 31.33 and its differential value f.
Based on the signal fed back from the path storage register 30, the expected value at that point in time is calculated, and the sign of the reproduced waveform is also corrected here and output to the metric calculators 24, 27.

Inside the metric calculator 24.27, estimated signals al, b are generated from the signal estimator 32.34 based on sample values e, f of the isolated waveform shown in FIG. A metric value, which is the error between the signals a and b from the sampler 23 and the sampler 26, is calculated using l.

FIG. 5(a), 01) shows the signal waveform input to the metric calculator 24.27 when the signal recorded on the magnetic medium to be reproduced by the head 21 is "1100I". The broken lines shown in FIG.
4 shows the sample value input.

Further, the solid line indicates an estimated value based on the isolated waveform stored in the impulse response memory 31, and aoI to a41 is a0
~a4 is shown as a sample value sampled at the same sampling interval T and input from the signal estimator 32 to the metric calculator 24. Similarly, the broken line shown in FIG. 5(b) indicates the input signal to the sampler 26 differentiated by the differentiator 25, and be-ba is input to the metric calculator 24 from the sampler 26 sampled at the sampling interval T. The solid line is an estimated value based on the isolated waveform stored in the impulse response memory 33, and b
(11~b4s is the same sampling interval T as ~b4)
The sample values sampled at and input from the signal estimator 34 to the metric calculator 27 are shown.

The calculated metric values are combined in an adder 28, and using the combined metric value g as the final metric, a path selector 29 selects m paths in descending order of this value. This selected path is input to the path storage register 30 as a signal. As the detection output, the value of the path with the smallest final metric among the oldest values in the path storage register 30 is selected. The detection output at this time is fed back to the signal estimators 32 and 34.

In addition, in the metric calculator 24.27, the sampler 23
and the sequence of input signals a and b from the sampler 26 and the assumed signal path (path storage register 30 and signal estimator 32
．． signal estimator 32 .
The distance to the estimated signal array a', b'' (digital values) created in step 34 is calculated as a metric, but this calculation is generally performed by a circuit equipped with a squarer 35 as shown in FIG. In the figure, a0 to a4 are input signals from the sampler, and aol to a41 are input signals from the signal estimator.

In the magnetic recording/reproducing apparatus configured as described above, the differential value differentiated by the differentiator 25 is O at the peak position of the head output.
This value does not change much even with modulation of the output signal, and stable detection is possible. and,
Since this signal alone cannot cope with the case where "0" continues in the recorded information, the signal amplitude is also detected at the same time in accordance with this differential value, as shown in FIG. These sampled values are compared with predicted values for the assumed input signal, and the sum of the squares of their respective errors is used as the decision metric.

In this way, in this embodiment, the differential signal of the head signal, which is less affected by the modulation of the head output signal, is detected in accordance with the conventional head output signal, and the values of the two signals are calculated as predicted values for the assumed input signal. By comparison, the error rate of data detection can be significantly reduced compared to the conventional method.

FIG. 6 shows the configuration of a magnetic recording/reproducing apparatus according to another embodiment of the present invention. This embodiment differs from the embodiment shown in FIG. 2 in that the metric values c and d outputted from the metric calculators 24 and 27 are weighted and then added by an adder 28. For this reason, in this embodiment, each K between metric calculator 24, 27 and adder 28 is
Coefficient units 41 and 42 for weighting I and Kz are provided, and only this point differs from the configuration of the magnetic recording/reproducing apparatus shown in FIG. Also in the device of this embodiment, the composite metric value g synthesized by the adder 28 is used as the final metric, and m paths are selected from the path selector 29 in order of decreasing value.
The selected path is input to the path storage register 30 as a signal. As the detection output, the value of the path with the smallest final metric is selected from among the oldest values of the path stored G-STAR 30.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to realize a detector with fewer errors in response to fluctuations in output signals caused by recording media specific to magnetic recording, and the excellent characteristics of the maximum likelihood detection method can also be applied to magnetic storage. There are effects that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of a magnetic recording/reproducing apparatus according to the present invention, FIG. 2 is a block circuit diagram showing the configuration of a magnetic recording/reproducing apparatus according to an embodiment of the present invention, and FIG. 3 is a diagram of the metric calculator of FIG. 2. A block circuit diagram showing the configuration, FIG. 4 is a waveform diagram explaining sample values stored in the impulse responder in FIG. 2, and FIG. 5 is a waveform diagram showing sample values input to the metric calculator in FIG. 2. FIG. 6 is a block circuit diagram showing the configuration of a magnetic recording/reproducing apparatus according to another embodiment of the present invention. 21... Magnetic head, 22... Filter, 23, 26... Sampler, 24, 27... Metric calculator, 25... Differentiator, 28... Adder, 29... Pass Selector, 30... Path storage register, 31, 33... Impulse response storage, 32, 34.
...Signal estimator.

Claims (1)

[Scope of Claims] 1. A magnetic recording and reproducing device that decodes a reproduced signal from a magnetic recording medium using a maximum likelihood detection method, and a signal processing circuit that generates a signal obtained by directly sampling the output signal from a magnetic head at bit intervals. (1), and at least one signal parallel processing circuit (2) that branches the output signal from the magnetic head, passes the branched signal through a filter, and then generates a signal sampled at similar bit intervals.
), a signal estimation circuit (3) that generates assumed data of each signal output from the signal processing circuit (1) and the signal parallel processing circuit (2), and the signal processing circuit (1) and the signal parallel processing a metric calculation circuit (4) that calculates a metric that is an error between each signal output from the circuit (2) and an estimated signal value based on assumed data from the signal estimation circuit (3); An addition circuit (5) that adds at least two metric values calculated in (4) to create a composite metric value; and a likelihood judgment circuit (6) that determines the likelihood based on the composite metric value from the addition circuit (5). ); A magnetic recording and reproducing device comprising: 2. When the addition circuit (5) adds at least two metric values calculated by the metric calculation circuit (4) to create a composite metric value, it adds weights to each of the two metric values. Claim 1
The magnetic recording/reproducing device described in . 3. The magnetic recording and reproducing apparatus according to claim 1 or 2, wherein the filter of the signal parallel processing circuit (2) has differential characteristics.